SPACECRAFT PROPULSION - KTH

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- 55 -Table 8 notes the differences between the propulsion performancereference numbers I sp (v e ) and I ssp . Hence, the differences becomes ofparticular interest with respect to the calculation of the ‘propulsionsystem mass fraction’, m SP /m SC . Usually this is done by taking intoaccount the rocket equation and calculating the mass of propellant,Eq. (9). However, taking into account the entire propulsion systemmass, the ‘propulsion system mass fraction’ has to be calculated withEq. (19), which is related to the I ssp .The differences in calculating the ‘propulsion system mass fraction’can be illustrated by the SMART-1 project (the first Europeanspacecraft DELTA-V travelled PERFORMANCES to and orbit OF the S/C Moon <strong>PROPULSION</strong> [14] [15]) SYSTEMS as noted inTable Calculated 8. Results by are System-spec. elucidated Impulse in diagram Equation Fig. versus 19 below. Rocket Equationm PS/m S/C0,400,350,300,250,20Mission to the Moon:delta-v=3.7 km/s(constant low thrust space manoeuvres)(1) Calculated by System-spec. Impulse EquationI ssp= 10 811 Ns/kgv e= 15 107 m/s(1)(2)0,150,100,050,00(2) Calculated by Rocket EquationI sp= 15 107 Ns/kgv e= 15 107 m/s0 1000 2000 3000 4000delta-v (m/s)Fig. 19: Delta-v Performance of Spacecraft Propulsion SystemDiagram Fig.19 shows clearly that for electric propulsion, where theelectric subsystem mass, m EL , may form a major ‘dead’ dry mass ofthe overall propulsion system mass, the ‘rocket equation’ does notapply alone.
- 56 -Table 9 presents a summary of the comparison between electrical(ion) and chemical (bipropellant) propulsion.Table 9: Comparison of typical electrical vs. chemical figuresType ofThrusterSpec. -Impulse(Ns/kg)Thrust F(N)DC PowerRequired(W)Electrical(Ion thruster)Chemical(Bipropellant)Order ofmagnitude ofthe ratioION/Chemical 30 00010 -3 – 0.2 400 – 800≈ 3 000 4 – 5004 – 8(short term)10 2Conclusion:- While chemical propulsion is limited to specific impulse exhaustvelocity of
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-iv -Standard NotationsStandard not
Page 8 and 9:
- 1 -1 INTRODUCTIONThis booklet sum
Page 10 and 11:
- 3 -The main features of jet propu
Page 12: - 5 -This expresses that the spacec
Page 17 and 18: - 10 -3.2.3 Evaluation of Mass of P
Page 19 and 20: - 12 -With regard to the system-spe
Page 21 and 22: - 14 -According to Fig. 3 and with
Page 23 and 24: - 16 -Historically, chemical propul
Page 25 and 26: - 18 -gases leave the outlet of the
Page 27 and 28: - 20 -The vaporising liquid system
Page 30 and 31: - 23 -Further, for vaporising liqui
Page 32 and 33: - 25 -ConclusionAlthough of moderat
Page 34 and 35: G- 27 -4.2.3 MonopropellantMonoprop
Page 36 and 37: - 29 -System-specific Impulse, I ss
Page 38 and 39: - 31 -Table 4: Ranges of typical Pr
Page 40 and 41: - 33 -4.2.4 BipropellantBipropellan
Page 42 and 43: - 35 -management devices), propella
Page 44 and 45: - 37 -From Eq. (41) it is obvious t
Page 46 and 47: - 39 -4.2.5 General System Design C
Page 48 and 49: - 41 -System-specific Impulse, I ss
Page 50 and 51: - 43 -4.3 Electric Propulsion4.3.1
Page 52 and 53: - 45 -To the above described catego
Page 54 and 55: - 47 -4.3.2 Propulsion System Desig
Page 56 and 57: - 49 -Fig.17, has to be considered
Page 58 and 59: - 51 -The term of an optimal exhaus
Page 60 and 61: - 53 -resulting in a maximum value
Page 64 and 65: - 57 -5 PROPULSION SYSTEMS SELECTIO
Page 66 and 67: - 59 -m PS/m S/C1,0I ssp=193 Ns/kg(
Page 68 and 69: - 61 -In considering the merits of
Page 70 and 71: - 63 -Table 11: Survey: Typical Can
Page 72 and 73: - 65 -6.1 Potential Improvement of
Page 74 and 75: - 67 -6.2 Potential Improvement of
Page 76 and 77: - 69 -6.3 New ApproachesNew approac
Page 78 and 79: - 71 -Extensive research has been p
Page 80 and 81: - 73 -8 MISSION SURVEILLANCE OFPROP
Page 82 and 83: - 75 -[9 W. Inden; “Development R
Page 84: Notes
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